98 points, just tryna give some away

How do you find principle and simple interest

Ricky takes out a $31,800 student loan to pay his expenses while he is in college. after graduation, he will begin making payments of $190.66 per month for the next 30 years to pay off the loan. how much more will ricky end up paying for the loan than the original value of $31,800? ricky will end up paying $ more than he borrowed to pay off the loan.

Can someone me with #s 8, 9, and 11. with just one of the three also works. prove using only trig identities.